(1) Field of the Invention
The present invention relates to a technology for obtaining a high-resolution video signal from a video signal, and in particular, it relates to a technology for achieving the high resolution, with increasing a number of pixels building up a video frame and removing unnecessary aliasing, while composing or combing a plural number of video frames.
(2) Description of the Related Art
In recent years, advancement is made on large sizing of the screen, for television receivers, and accompanying with this, it is common that the video signal inputted from broadcasting, communication and/or storage medium, etc., is not displayed on it as it is, but is displayed with increasing the pixel numbers in the horizontal/vertical directions through digital signal processing. In this instance, however, it is impossible to increase the resolution only by increasing the pixel number, through an interpolation low-pass filter using sinc function or spline function, being well-know in general.
Then, as is already described in a reference document 1, there is proposed a technology (hereinafter, the conventional art) for increasing the pixel number while achieving the high resolution at the same time, by composing or synthesizing a plural number of picture or video frames (hereinafter, being called only “frame”, in brief). With this conventional art, the high resolution can be obtained through three processes, (1) motion estimation, (2) broadband interpolation, and (3) a weighted sum. Herein, the (1) motion estimation is a process for assuming or estimating difference in the sampling phase (or sampling position) for each video data, with using the each video data of the plural number of video frames inputted. The (2) broadband interpolation is a process for increasing the pixel number (i.e., sampling points) of the each video data, including the aliasing components therein, through interpolation, with use of a wideband low-pass filter for transmitting all of the high-frequency components of an original signal, thereby obtaining high resolution of the video data. The (3) weighted sum is a process for negating the aliasing components generated when sampling the pixels, by taking the weighted sum depending on the sampling phase of each high-density data, so as to remove them, and at the same time restoring the high-frequency components of the original signal.
FIGS. 2(a) to 2(e) shows this high-resolution technology, in brief. As is shown in FIG. 2(a), herein it is assumed that a frame #1 (201), a frame #2 (202) and a frame #3 (203) on different time axes are inputted, to be composed with, thereby obtaining an output frame (206). For the purpose of simplification, first of all, consideration is paid upon case where the target moves into the horizontal direction (204), i.e., achieving the high resolution through a linear signal processing on a horizontal line (205). In this instance, as is shown in FIGS. 2(b) and 2(d), between the frame #2 (202) and the frame #1 (201) is generated a positional difference depending on an amount of moving (204) of the target. This positional difference is obtained through the (1) motion estimation mentioned above, thereby to make such motion compensation (207) upon the frame #2 (202) that no positional difference is generated, as is shown in FIG. 2(c), and at the same time, phase difference θ is obtained between the sampling phases (209) and (210) of pixels (208) for each frame. Through conducting the (2) broadband interpolation and the (3) weighted sum mentioned above, upon this phase difference θ (211), a new pixel (212) can be produced at a position just between the original pixels (208) (i.e., phase difference θ=π); thereby achieving the high resolution. Herein, as a technology of achieving such the (1) motion estimation mentioned above, a large number of methods are already proposed, as described in reference documents 2 and 3, for example, and it can be applied as it is. The (2) broadband interpolation can be achieved by means of a general low-pass filter, having pass band doubled to Nyquist frequency, as is described in the reference document 1. The (3) weighted sum will be mentioned later. However, in actual, it must be also considered that the movement of the target includes, not only the parallel movement, but also accompanying movements of rotation, expansion and reduction, etc.; however, in case where the time distance between the frames is very small and/or when the target moves slowly, it is possible to consider those movements with approximating them into a local parallel movement.    (Reference Document 1) Shin AOKI “Super Resolution Processing by Plural Number of Lower Resolution images”, Ricoh Technical Report pp. 19-25, No. 24, NOVEMBER, 1998;    (Reference Document 2) Shigeru ANDO “A Velocity Vector Field Measurement System Based on Spatio-Temporal Image Derivative”, Papers of Measurement Automatic Control Academic Society, pp. 1330-1336, Vol. 22, No. 12, 1986; and    (Reference Document 3) Hiroyuki KOBAYASHI et al. “Calculation Method of a Phase-Only Correlation Function for Images Based on Discrete Cosine Transform”, IEICE Technical Report ITS2005-92, IE2005-299(2006-02), pp. 73-78.